The global head of Citigroup's environmental and social risk management was found dead in his New York apartment on Tuesday with his throat cut and investigators said late on Wednesday it was a suicide, according to media reports.
The body of Mr Shawn Miller, 42, was discovered in the bathtub of his apartment in Manhattan's Financial District and police initially believed a third-party was responsible after finding no weapon.
However, after moving Mr Miller, police discovered a knife beneath his body in the bathtub, the New York Daily News reported.
Investigators had been trying to find a man with whom Mr Miller was seen walking into the apartment at 120 Greenwich St at about 6.30pm Monday night. The man later left alone.
There were no signs of forced entry.
A doorman discovered his body at about 3pm on Tuesday after a worried friend called to ask if he could check on Mr Miller.
Police said Wednesday they found drug and alcohol in the apartment, including what they believed to be crystal meth.
Investigators say Mr Miller had hooked up with a stranger for sex Monday using the website Backpage.com.
Mr Miller, who joined Citigroup in 2004, worked on sustainability matters, including mining and renewable energy policies.
Colleagues described him to the Wall Street Journal as candid, fair and a passionate defender of human rights, and said that those inside the bank were shocked and saddened by his death. Citigroup brought grief counselors to the bank's Tribeca offices this week.
Mr Miller also formerly worked for the World Bank Group's International Finance Corporation.